The second ability of Garruk, the Veil-Cursed doesn’t target a creature. However, when that ability resolves, you must sacrifice a creature if you control one.

9/22/2011

The number of creature cards in your graveyard is counted when the third ability of Garruk, the Veil-Cursed resolves. Once the ability resolves, the bonus doesn’t change if that number changes later in the turn.

9/22/2011

Only creatures you control when the third ability of Garruk, the Veil-Cursed resolves will receive the bonus. Creatures that enter the battlefield or that you gain control of later in the turn won’t be affected.